Add module on numerical modeling

[mdpiper]

This topic got cut last year because of changes due to COVID-19, but it should be a part of ESPIn. Suggested topics include

• grid types
• discretization
• explicit and implicit solutions
• solvers
• stability

but I defer to whatever @BCampforts wants to cover.

[mdpiper]

@BCampforts I know we've discussed this, but would you be willing to lead the development of this module? I'll help wherever you want me to.

[mdpiper]

We're going to defer this. @BCampforts does some of this in his Python for ESP Scientists section.

[mdpiper]

@gregtucker brought up the need for training on this topic in a discussion today.

[mcflugen]

There is a notebook and a set of slides from our CSDMS 2022 clinic that may be helpful for this.